The present invention relates to a tensioner pad assembly, for mounting on an endless track of a tensioner to engage an elongated product supported by the tensioner. The invention furthermore relates to a tensioner provided with such pad assemblies, a vessel provided with such a tensioner and the use of such a tensioner.
Tensioners are known from the prior art, for example from WO2009088287 and WO2008007945. Tensioners are for example used in the offshore industry for handling an elongated product from an offshore vessel, such as laying a pipeline for transportation of hydrocarbons (oil, gas, etc.) from board a vessel on the seabed. Tensioners are used for many pipelaying techniques, such as S-lay, Reel lay, J-lay, but may also be embodied and/or used for handling other elongated products, for example hydrocarbon risers, electrical cables, fiberglass cables, umbilicals (e.g. for subsea equipment, ROV, geosurveying tooling, etc) and coiled tubing.
A tensioner is adapted to absorb the load exerted by the elongated product on the tensioner, i.e. to support the weight of the launched product. This is achieved by frictionally clamping the elongated product between multiple track units, the track units comprising endless tracks with gripping pads mounted thereon, to support and move the elongate product. Tensioner having a large “load holding capacity” and in the field capacities of tens of tonnes, or even well over 100 tonnes, for a tensioner are not uncommon.
In a known embodiment a tensioner comprises a tensioner frame and multiple track units mounted in that frame defining an product passage having a passage axis extending axially, and preferably centrally, through the tensioner frame. The number of track units is normally adapted to the capacity and/or product type and common tensioner designs include two, three or four track units (or possibly a variable number of track units).
Each track unit includes a chassis, an endless track supported by the chassis, e.g. with support rollers or other bearing means being mounted on the chassis for supporting the endless track, and a track motion control device for effecting controlled motion of the endless track. The endless track is provided with a multitude of tensioner pads for engaging the elongated product.
It is known to arrange each track unit mobile within the tensioner frame so that the “gap” or “pipeline passage” between the tracks can be adapted to different pipeline diameters. Between the chassis of each track unit and the tensioner frame a connecting structure is provided that at least allows for lateral motion of the track unit with respect to the passage axis so as to adapt the position of the track unit.
Furthermore, the tensioner is provided with squeeze actuators, such as hydraulic cylinders, to create the “squeeze pressure” between the track units and the exterior of the elongated product by pushing the track units towards the product passage. This squeeze pressure is needed to hold the elongated product and absorb the load of the elongated product on the basis of friction.
It will be understood that the “squeeze pressure” needed between the elongated product and the tracks is very significant as the resultant frictional force between grip pads and elongate product might need to be several tens of tonnes, or even well over one hundred tonnes. Frictionally clamping the elongate product furthermore requires an optimal interface between the tensioner and the elongated product, i.e. the pads provided on the track units, engaging the elongate product should match, at least to a certain extent, the circumference, which with most elongate products is defined by the diameter, of the elongate product.
Since typically a pad is adapted to fit a particular type of elongate product, i.e. an elongate product with a particular diameter, a change of product diameter often requires all the pads provided on the tensioner tracks to be replaced. Thus, numerous pads and have to be loosened, replaced and fixed to enable use of the tensioner with a product having a different diameter. A serious handicap of this is the down-time caused by the necessary changeover from one pipe diameter to another. In addition, many types of pads need to be available, and thus on storage, to allow for optimal usage of the tensioner.
It is furthermore noted that tensioners, in particular when used in pipe laying, are often mounted in positions that are not easy accessible, for example high above the working deck of a pipe laying vessel. Thus, replacing the pads on a tensioner not only requires personal to get access to these hard to reach tensioners, but also transporting the new pads to, and the replaced pads from, these locations.
The present invention aims to propose an alternative to the pads used in prior art tensioners. Another object of the invention is to provide a tensioner pad assembly that obviates or at least reduces to a certain extent the abovementioned drawbacks.